Patterned materials, such as obtained through the directed self-assembly (DSA) of block copolymers, has been proposed for making etch masks. DSA of block copolymers uses guiding features in a sublayer to direct the block copolymer film formation. After the block copolymer components self-assemble on the sublayer, one of the polymer blocks can be selectively removed, leaving the other block with the desired pattern. This patterned block can in turn be used as an etch mask to transfer the pattern into an underlying substrate (100); for example for use in semiconductor manufacturing, such as in manufacturing dynamic random-access memory (DRAM) devices. However, it was reported that the DSA patterned block copolymer lines do not yet meet the semiconductor industry specification for the line edge roughness, i.e. a measure for the deviation between the actual shape of a pattern feature sidewall and its intended shape (typically quantified as 3 times the standard deviation from the intended shape), and line width roughness, i.e. a measure for the deviation between the actual width of a pattern feature and its intended width (typically quantified as 3 times the standard deviation of the width).
In order to improve the etch selectivity for the block copolymer, a more recent approach, called sequential infiltration synthesis (SIS), was developed for selectively hardening one type of the block copolymer sections by infusing it with an inorganic material. In one example of SIS, a poly(styrene-block-methyl methacrylate) (PS-b-PMMA) block copolymer is self-assembled onto a substrate to form a pattern of the block copolymer sections. A trimethylaluminium (TMA) inorganic precursor is then introduced and infiltrates the PMMA, but does not react with the PS. Subsequently, an oxidant such as water is introduced to finish the reaction, thereby forming the alumina inorganic material in the locations in the PMMA where the TMA attached. This infiltration of the precursor and formation of the inorganic material is typically repeated until a desired level of infusion has been reached. Finally, the PS is removed, leaving a pattern that generally replicates the original pattern of the PMMA but that is now hardened by the inorganic material. This hardening typically improves the line edge roughness, the line width roughness and the etch resistance, as compared to the initial polymer sections, and thus makes the hardened pattern a more suitable etch mask.
However, after PS removal and pattern transfer, pitch walking, i.e. a systematic and periodic change in the pitch compared to the original pitch, is typically observed in the transferred pattern, thereby causing any further pattern that is transferred into the substrate to differ from that original pattern. Thus, there is still a need within the art for patterned structures, and methods for the fabrication thereof, comprising a pattern of hardened material which can be transferred more correctly into underlying layers.